Edition utilisateur Admin

Bonjour,

Voila je rencontre un petit problème avec mon code.

Je souhaiterais pouvoir modifier un utilisateur via mon backoffice mais sans être obligé de modifier le mot de passe

Voici mon userType

public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('email', EmailType::class, [
                'label' => 'Email',
                'required' => true,
                'attr' => ['class' => 'form-control']
            ])
            ->add('username', TextType::class, [
                'label' => 'Utilisateur',
                'required' => true,
                'attr' => ['class' => 'form-control']
            ])
            ->add('plainPassword', RepeatedType::class, array(
                'type' => PasswordType::class,
                'first_options'  => array(
                    'label' => 'Mot de passe',
                    'required' => true,
                    'attr' => [
                        'class' => 'form-control',
                        'minlength' => 12
                        ]
                ),
                'second_options' => array(
                    'label' => 'Repeter mot de passe',
                    'required' => true,
                    'attr' => [
                        'class' => 'form-control',
                        'minlength' => 12
                        ]
                ),
            ))
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => User::class,
        ));
    }

Voici mon AdminUserController

class AdminUserController extends AbstractController
{
    /**
     * @var UserRepository
     */
    private $repository;

    /**
     * @var ObjectManager
     */
    private $em;

    public function __construct(UserRepository $repository, ObjectManager $em)
    {
        $this->repository = $repository;
        $this->em = $em;
    }

    /**
     * @Route("/admin/user-list", name="admin.users.list")
     */
    public function index()
    {
        $users = $this->repository->findAll();

        return $this->render('admin/user/index.html.twig', ['users' => $users]);
    }

    /**
     * @Route("/admin/user-edit/{id}", name="admin.users.edit", methods="GET|POST")
     * @param User $user
     * @param Request $request
     * @return \Symfony\Component\HttpFoundation\Response
     */
    public function edit(User $user, Request $request)
    {
        $userName = $user->getUsername();

        $form = $this->createForm(UserType::class, $user);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            $this->em->flush();
            $this->addFlash('success', 'Utilisateur modifié avec succés');
            return $this->redirectToRoute('admin.users.list');
        }

        return $this->render('admin/user/edit.html.twig', [
            'username' => $userName,
            'form' => $form->createView()
        ]);
    }
}

Et enfin mon template :

{{ form_start(form) }}
<div class="row">
    <div class="col-md-3">
        <div class="form-group">
            {{ form_row(form.email) }}
        </div>
    </div>
    <div class="col-md-3">
        <div class="form-group">
            {{ form_row(form.username) }}
        </div>
    </div>
</div>
{{ form_widget(form) }}
<button class="btn btn-primary">{{ button|default('Editer') }}</button>
{{ form_end(form) }}